Parodia ottonis

Parodia ottonis is a small cactus. It belongs to the Cactaceae family. Kew gives its native range as southern Brazil to northeastern Argentina. The RHS lists Uruguay too. It grows in subtropical grasslands. It stays green all year. You may also find it named Notocactus ottonis. It suits pots and bright rooms indoors. It also suits greenhouses and conservatories.

The stem forms a ball or an upright cylinder. The RHS gives its garden height and spread as 0.3–1.6 feet [0.1–0.5 metres]. Plants take about five to ten years to reach full size. Each stem can measure 0.5 feet [0.15 metres] across. The stem has six to twelve ribs, at times fifteen. Fine spines leave much of its surface in view. They may grow straight, bend, or twist. Some are white, yellow, or pink. Others are brown or black. The longest central spines reach about 0.13 feet [0.04 metres].

Yellow flowers open at the crown in summer. Each can span about 0.2 feet [0.06 metres]. LLIFLE says this species blooms with ease. Its seeds are glossy black and shaped like bells. They have a bumpy surface. A fruit may hold fifteen to one hundred seeds. Growers can sow seed in spring or summer. They can also grow new plants from offsets, or side shoots. Both ways help growers build a pot collection.

Give this cactus full sun or bright, filtered light. Use cactus compost that drains well. Sandy or loamy mixes suit it. The pH should be acid to neutral. LLIFLE favours mixes rich in minerals, with little organic matter. Rich compost can cause stretched growth. Water while the plant grows. Let the mix dry between drinks. Keep it dry through its cool winter rest. Feed every six to eight weeks while it grows. Use liquid fertiliser low in nitrogen. The pot must drain well. LLIFLE suggests a new pot every two years.

The RHS gives its cold tolerance as H2. This points to a need for frost-free care. Yet LLIFLE reports that dry plants can stand brief frost. LLIFLE advises winter temperatures of 5–15°C. It also calls for low humidity, or dry air. Wet conditions in winter can cause rot while plants rest. The RHS reports few disease problems with the right care. Watch for mealybugs and aphids, which may attack plants. It needs no pruning. This makes it a pot plant that needs little care.